Blowby gas ventilation system for supercharger-equipped internal combustion engine

ABSTRACT

A blowby gas ventilation system for a supercharger-equipped internal combustion engine, which discharges blowby gas from a crankcase into intake air, includes a positive crankcase ventilation passage through which the blowby gas is delivered from the crankcase to an intake passage. The positive crankcase ventilation passage branches, in an intermediate location in the positive crankcase ventilation passage, into a first path that is used during natural aspiration of the internal combustion engine and a second path that is used during supercharging of the internal combustion engine, and a part of the positive crankcase ventilation passage, which includes a branching portion between the first path and the second path, is formed integrally with a cylinder head of the internal combustion engine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a blowby gas ventilation system for asupercharger-equipped internal combustion engine.

2. Description of Related Art

As a blowby gas ventilation system that discharges blowby gas from acrankcase, there is known a system described in Japanese PatentApplication Publication No. 2009-250159 (JP 2009-250159 A). In theblowby gas ventilation system described in JP 2009-250159 A, a part of apositive crankcase ventilation (PCV) passage through which blowby gasflows from the crankcase to an intake passage, and an oil separatorchamber that separates an oil component from blowby gas are formedintegrally within a cylinder head.

During natural aspiration of the internal combustion engine, blowby gasin the crankcase can be discharged by sucking blowby gas from thecrankcase into the PCV passage formed to connect an area downstream ofthe throttle valve in the intake passage to the crankcase, by usingnegative intake pressure caused downstream of the throttle valve.However, in the case of a supercharger-equipped internal combustionengine, during supercharging, positive pressure is caused in the areadownstream of the throttle valve in the intake passage, and thus, it isnot possible to discharge blowby gas in the aforementioned manner, thatis, it is not possible to discharge blowby gas through the use of intakenegative pressure. In this regard, in the aforementioned related-artblowby gas ventilation system, consideration is not given to thedischarging of blowby gas from the crankcase during supercharging, andtherefore blowby gas can be discharged from the crankcase only duringnatural aspiration.

SUMMARY OF THE INVENTION

The invention provides a blowby gas ventilation system for asupercharger-equipped internal combustion engine, which is able todischarge blowby gas both during supercharging and during naturalaspiration, while complication of the configuration thereof issuppressed.

An aspect of the invention relates to a blowby gas ventilation systemfor a supercharger-equipped internal combustion engine, which is appliedto an internal combustion engine including a supercharger, and whichdischarges blowby gas from a crankcase into intake air. The blowby gasventilation system includes a positive crankcase ventilation passagethrough which the blowby gas is delivered from the crankcase to anintake passage. The positive crankcase ventilation passage branches, inan intermediate location in the positive crankcase ventilation passage,into a first path that is used during natural aspiration of the internalcombustion engine and a second path that is used during supercharging ofthe internal combustion engine, and a part of the positive crankcaseventilation passage, which includes a branching portion between thefirst path and the second path, is formed integrally with a cylinderhead of the internal combustion engine.

In the foregoing blowby gas ventilation system, a portion of the PCVpassage which extends from the crankcase to the cylinder head is sharedby the two paths that are used during natural aspiration and duringsupercharging, and that form the PCV passage. Therefore, theconfiguration is made simpler. Thus, it is possible to discharge theblowby gas both during supercharging and during natural aspiration whilesuppressing complication of the configuration.

During supercharging, an increased amount of blowby gas needs to bedischarged from the crankcase, and thus, the amount of oil carried awayby the blowby gas increases. In this regard, when the downstream-sideopening of the first path in the cylinder head is formed in the sidesurface of the cylinder head and the downstream-side opening of thesecond path in the cylinder head is formed in the upper surface of thecylinder head, the second path extends upward from the branchingportion. Thus, due to the action of gravity, an increased amount of oilis separated from the blowby gas that flows in the second path, andtherefore the amount of oil carried away by the blowby gas can bereduced.

During supercharging, the blowby gas may be discharged, for example, byan ejector provided in a circulation passage through which intake airflows from an area downstream of the supercharger to an area upstream ofthe supercharger. In this case, when the ejector is fitted to a headcover, the second path can be connected to the ejector, withoutextending outside the internal combustion engine. Thus, theconfiguration is made simpler.

Furthermore, an enlarged chamber may be formed in the part of thepositive crankcase ventilation passage, and a flow passage area of theenlarged chamber, through which the blowby gas flows, may be larger thanthat of an upstream portion of the part of the positive crankcaseventilation passage, the upstream portion being located upstream of theenlarged chamber. In this case, oil is separated from the blowby gas dueto changes in flow speed caused when the blowby gas flows into theenlarged chamber and when the blowby gas flows out of the enlargedchamber, and thus, the amount of oil carried away by the blowby gas canbe reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the invention will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a diagram schematically showing an entire configuration of ablowby gas ventilation system for a supercharger-equipped internalcombustion engine according to an embodiment of the invention;

FIG. 2 is a diagram showing the position of an in-head passage in acylinder head in the blowby gas ventilation system according to theembodiment;

FIG. 3 is a perspective view showing a perspective-view structure of thein-head passage in the blowby gas ventilation system according to theembodiment;

FIG. 4 is a side view of a side-view structure of the in-head passage inthe blowby gas ventilation system according to the embodiment;

FIG. 5 is a diagram showing flows of air and blowby gas in the blowbygas ventilation system according to the embodiment during naturalaspiration of the internal combustion engine; and

FIG. 6 is a diagram showing flows of air and blowby gas in the blowbygas ventilation system according to the embodiment during superchargingof the internal combustion engine.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a blowby gas ventilation system for a supercharger-equippedinternal combustion engine according to an embodiment of the inventionwill be described in detail with reference to FIG. 1 to FIG. 6. As shownin FIG. 1, a cylinder block 12 of the internal combustion engine isprovided with cylinders 11 in each of which a piston 10 is disposed sothat the piston 10 is able to reciprocate. On an upper portion of thecylinder block 12, there is provided a cylinder head 13. On an upperportion of the cylinder head 13, a head cover 14 is provided. On theother hand, at a lower portion of the cylinder block 12, there is formeda crankcase 15. An oil pan 16 that stores lubricating oil of theinternal combustion engine is fitted to a lower portion of the crankcase15.

In an intake passage 20 of the internal combustion engine, there areprovided, in order from the upstream side, an air cleaner 21 thatfilters air introduced into the intake passage 20, a compressor 22 of aturbocharger, which is an exhaust-driven supercharger, an intercooler 23that cools air whose temperature has been increased by supercharging,and a throttle valve 24 that adjusts the intake air flow rate. Theintake passage 20 is connected to the cylinder head 13 via an intakemanifold 25 that is provided downstream of the throttle valve 24.

The supercharger-equipped internal combustion engine described above isprovided with a blowby gas ventilation system that discharges blowby gasthat has leaked into the crankcase 15 through a space between thesliding contact surfaces of the pistons 10 and the cylinders 11. Theblowby gas ventilation system includes a fresh air introduction passagethrough which fresh air is introduced into the crankcase 15 during thedischarging of blowby gas, and a positive crankcase ventilation (PCV)passage through which blowby gas is delivered from the crankcase 15 tothe intake passage 20. Of these two passages, the fresh air introductionpassage is formed by a fresh air introduction pipe 30 and a fresh airintroduction passage 31. The fresh air introduction pipe 30 connects anarea downstream of the air cleaner 21 in the intake passage 20, to ahead cover 14. The fresh air introduction passage 31 is formed in thecylinder head 13 and the cylinder block 12 so as to providecommunication between the inside of the head cover 14 and the crankcase15.

On the other hand, the PCV passage of the blowby gas ventilation systemis configured as follows. That is, an in-block passage 32 is formedwithin the cylinder block 12. The in-block passage 32 is formed so as toextend through the cylinder block 12 from the crankcase 15 to an uppersurface of the cylinder block 12. Furthermore, in an intermediatelocation in the in-block passage 32, there is provided an oil separator33 that removes an oil content from the blowby gas that flows inside theoil separator 33. In this embodiment, the oil separator 33 employed is acyclone separator that separates an oil content from blowby gas bycentrifugal separation that is performed by causing swirl flows insidethe oil separator 33.

The in-block passage 32 is connected to an in-head passage 34 that isformed within the cylinder head 13. In the in-head passage 34, the PCVpassage branches into a first path 35 that is used during naturalaspiration of the internal combustion engine, and a second path 36 thatis used during supercharging. The first path 35 is connected to theintake manifold 25 via a PCV valve 37. The PCV valve 37 opens and closesaccording to the differential pressure across the PCV valve 37, andprevents fresh air from reversely flowing from the intake manifold25-side to the crankcase 15-side, and adjusts the flow rate of blowbygas introduced into intake air. On the other hand, the second path 36 isconnected to an ejector 38 that is fitted to an inside of the head cover14. The ejector 38 is provided in an intermediate location in acirculation passage 39 that provides communication between areasdownstream and upstream of the compressor 22 in the intake passage 20.The ejector 38 functions as a jet pump that sucks in blowby gas from thecrankcase 15 by using the stream of air flowing in the circulationpassage 39. A connecting position which is located upstream of thecompressor 22, and at which the circulation passage 39 is connected tothe intake passage 20 is downstream of a connecting position at whichthe fresh air introduction pipe 30 is connected to the intake passage20.

As shown in FIG. 2, the in-head passage 34 constituting a part of thePCV passage, which includes a branching portion between the first path35 and the second path 36, is formed between intake ports 40 of twoadjacent cylinders. As shown in FIG. 3, the in-head passage 34 extendsupward from a lower surface of the cylinder head 13, and is connected toan enlarged chamber 41. The enlarged chamber 41 is formed so that theflow passage area of the enlarged chamber 41, through which blowby gasflows, is larger than that of an upstream portion of the in-head passage34, the upstream portion being located upstream of the enlarged chamber41 (hereinafter, the upstream portion will be referred to as apre-branching passage 42). The enlarged chamber 41 functions as an oilseparator that separates an oil content from blowby gas due to change ina flow speed resulting from change in the flow passage area. From theenlarged chamber 41, a natural aspiration-range passage 44 that formsthe first path 35 extends obliquely upward, and supercharging-rangepassages 45 that form the second path 36 extend upward. In this blowbygas ventilation system, because of the restriction on the diameter of ahole that can be formed in the cylinder head 13, a portion of thein-head passage 34, which forms the second passage 36, is formed by thetwo supercharging-range passages 45 in order to secure a necessary flowpassage area.

As shown in FIG. 4, a downstream-side opening of the naturalaspiration-range passage 44 is formed in a side surface of the cylinderhead 13 (more specifically, a fitting surface 43 to which the intakemanifold 25 is fitted). The natural aspiration-range passage 44 isprovided with the PCV valve 37. On the other hand, downstream-sideopenings of the supercharging-range passages 45 are formed in the uppersurface of the cylinder head 13, to which the head cover 14 is fitted.The natural aspiration-range passage 44 and the enlarged chamber 41 ofthe in-head passage 34 are formed by core molding at the time of castingthe cylinder head 13. The supercharging-range passages 45 and thepre-branching passage 42 are formed by a boring process after thecasting process.

Next, operation of the blowby gas ventilation system for asupercharger-equipped internal combustion engine configured as describedabove will be described. As shown in FIG. 5, during the naturalaspiration of the internal combustion engine, negative pressure iscaused in the area downstream of the throttle valve 24 in the intakepassage 20. At this time, the PCV valve 37 opens due to the differentialpressure across the PCV valve 37. Due to the negative pressure in theintake manifold 25, blowby gas is sucked from the crankcase 15 into theintake manifold 25 via the in-block passage 32, the oil separator 33,the in-head passage 34, the natural aspiration-range passage 44 and thePCV valve 37. Furthermore, when blowby gas is discharged from thecrankcase 15 in this manner, air in the intake passage 20 is introducedinto the crankcase 15 via the fresh air introduction pipe 30 and thefresh air introduction passage 31. At this time, the pressure differencebetween the areas upstream and downstream of the compressor 22 in theintake passage 20 is small, and therefore air does not flow in thecirculation passage 39, so that the ejector 38 does not operate.

On the other hand, during the supercharging of the internal combustionengine, the pressure in the area downstream of the compressor 22 in theintake passage 20 becomes higher than the pressure in the area upstreamof the compressor 22 in the intake passage 20. At this time, a largepressure difference occurs between the areas upstream and downstream ofthe compressor 22 in the intake passage 20, and therefore, air flows inthe circulation passage 39, so that the ejector 38 operates due to thestream of air. As shown in FIG. 6, due to the operation of the ejector38, blowby gas is sucked from the crankcase 15 into the ejector 38 viathe in-block passage 32, the oil separator 33, the in-head passage 34and the second path 36. The blowby gas sucked into the ejector 38 isdelivered into intake air in the area upstream of the compressor 22 inthe intake passage 20, together with air flowing in the circulationpassage 39. At this time, the PCV valve 37 is in a closed state, andthus, it is possible to prevent reverse flow of air from the intakemanifold 25, in which the pressure has become high due to supercharging,into the crankcase 15.

During supercharging, the amount of blowby gas that leaks into thecrankcase 15 is large, and therefore the large amount of blowby gasneeds to be discharged from the crankcase 15. Then, if the flow rate ofblowby gas discharged from the crankcase 15 increases, the amount of oilcarried away by blowby gas also increases. In this regard, in thisblowby gas ventilation system, the second path 36 through which blowbygas flows during supercharging extends upward in a vertical direction(i.e., extends in a direction opposite to the direction of gravity).Thus, gravity acts in a direction opposite to a direction in whichblowby gas flows in the second path 36. Therefore, due to the action ofgravity, an increased amount of oil is separated from blowby gas thatflows in the second path 36, and therefore the amount of oil carriedaway by blowby gas can be reduced.

The above-described blowby gas ventilation system for thesupercharger-equipped internal combustion engine has the followingadvantageous effects. (1) In this embodiment, the PCV passage thatdelivers blowby gas from the crankcase 15 to the intake passage 20branches, in an intermediate location in the PCV passage, into the firstpath 35 that is used during natural aspiration of the internalcombustion engine and the second path 36 that is used during thesupercharging of the internal combustion engine. A part (the in-headpassage 34) of the PCV passage, which includes the branching portion(the enlarged chamber 41) between the first path 35 and the second path36, is formed integrally with the cylinder head 13. In this embodiment,a portion of the PCV passage, which extends from the crankcase 15 to thecylinder head 13, is shared by the two paths (the first and second paths35, 36) that are used during natural aspiration and duringsupercharging, and that form the PCV passage. Therefore, a hose, a pipe,or the like is not required and the number of component parts isreduced. Accordingly, it is possible to discharge blowby gas from thecrankcase both during supercharging and during natural aspiration whilesuppressing the complication of the configuration.

(2) In this embodiment, the downstream-side opening of the first path 35(the natural aspiration-range passage 44) in the in-head passage 34 isformed in the side surface of the cylinder head 13 (the fitting surface43 to which the intake manifold 25 is fitted), and the downstream-sideopening of the second path 36 (the supercharging-range passages 45) inthe in-head passage 34 is formed in the upper surface of the cylinderhead 13. Therefore, the second path 36 extends upward in the verticaldirection from the enlarged chamber 41 that is the branching portion ofthe PCV passage, that is, the second path 36 extends in the directionopposite to the direction of gravity. Thus, in the second path 36,blowby gas flows in the direction opposite to the direction in whichgravity acts. Therefore, it is possible to suppress an increase in theamount of oil carried away by blowby gas when supercharging isperformed, that is, when an increased amount of blowby gas needs to bedischarged from the crankcase.

(3) In this embodiment, the ejector 38 is fitted to the head cover 14,and the second path 36 is connected directly to the ejector 38, withoutextending outside the internal combustion engine. This eliminates theneed for a hose, a pipe or the like for connecting the second path 36 tothe ejector 38, and therefore makes the configuration simpler.

(4) In this embodiment, in the in-head passage 34, the enlarged chamber41 is formed, and the flow passage area of the enlarged chamber 41 islarger than the flow passage area of each of the upstream and downstreamportions located upstream and downstream of the enlarged chamber 41.Therefore, oil is separated from blowby gas due to changes in flow speedcaused when blowby gas flows into the enlarged chamber 41 and whenblowby gas flows out of the enlarged chamber 41, and thus, the amount ofoil carried away by blowby gas can be reduced.

The embodiment may be implemented with the following modifications.Although in the embodiment, the two supercharging-range passages 45 areprovided, only one supercharging-region passage 45 may be provide, if itis possible to form a passage that has a sufficiently large diameter, ina cylinder head 13.

Although in the embodiment, the enlarged chamber 41 for separating oilis formed in the in-head passage 34, the enlarged chamber 41 may beomitted if the amount of oil carried away by blowby gas can besufficiently reduced without providing the enlarged chamber 41.

Although in the embodiment, the ejector 38 is fitted to the inside ofthe head cover 14, the ejector 38 may be fitted to an outside of thehead cover 14. In such a case as well, it is possible to connect thesecond path 36 to the ejector 38 without providing a hose or a pipe thatextends outside the internal combustion engine.

Although in the embodiment, the ejector 38 is fitted to the head cover14, the ejector 38 may also be fitted to a site other than the headcover 14 if it is difficult to fit the ejector 38 to the head cover 14due to the layout of the circulation passage 39.

Although in the embodiment, blowby gas is discharged by using theejector 38 during supercharging, blowby gas may be discharged by anothermethod, for example, by using an electric pump or the like duringsupercharging. Although in the embodiment, the downstream-side openingof the first path 35 in the in-head passage 34 is formed in the sidesurface of the cylinder head 13 and the downstream-side opening of thesecond path 36 in the in-head passage 34 is formed in the upper surfaceof the cylinder head 13, the downstream-side openings may be formed atother sites on the cylinder head 13.

1. A blowby gas ventilation system for a supercharger-equipped internalcombustion engine, which is applied to an internal combustion engineincluding a supercharger, and which discharges blowby gas from acrankcase into intake air, the blowby gas ventilation system comprisinga positive crankcase ventilation passage through which the blowby gas isdelivered from the crankcase to an intake passage, wherein the positivecrankcase ventilation passage branches, in an intermediate location inthe positive crankcase ventilation passage, into a first path that isused during natural aspiration of the internal combustion engine and asecond path that is used during supercharging of the internal combustionengine, and a part of the positive crankcase ventilation passage, whichincludes a branching portion between the first path and the second path,is formed integrally with a cylinder head of the internal combustionengine; wherein a downstream-side opening of the first path in thecylinder head is formed in a side surface of the cylinder head, and adownstream-side opening of the second path in the cylinder head isformed in an upper surface of the cylinder head, and the second pathextends upward from the branching portion.
 2. The blowby gas ventilationsystem according to claim 1, wherein the blowby gas is discharged viathe second path by sucking the blowby gas using an ejector provided in acirculation passage through which the intake air flows from an areadownstream of the supercharger to an area upstream of the supercharger,and the ejector is fitted to a head cover.
 3. The blowby gas ventilationsystem according to claim 1, wherein an enlarged chamber is formed inthe part of the positive crankcase ventilation passage, and a flowpassage area of the enlarged chamber, through which the blowby gasflows, is larger than that of an upstream portion of the part of thepositive crankcase ventilation passage, the upstream portion beinglocated upstream of the enlarged chamber.